Add `time_compat` module

This module, obtained from Erlang 18.0 ERTS examples, allows to use the
new Time and Time Correction API introduced in Erlang 18.0 and fallback
to the old API (the deprecated `erlang:now()`) when running on older
Erlang.

References #233.

1 files changed, 305 insertions, 0 deletions

diff --git a/src/time_compat.erl b/src/time_compat.erl
new file mode 100644
index 0000000000..b87c6cc550
--- /dev/null
+++ b/src/time_compat.erl
@@ -0,0 +1,305 @@
+%%
+%% %CopyrightBegin%
+%% 
+%% Copyright Ericsson AB 2014-2015. All Rights Reserved.
+%% 
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%% 
+%% %CopyrightEnd%
+%%
+
+%%
+%% If your code need to be able to execute on ERTS versions both
+%% earlier and later than 7.0, the best approach is to use the new
+%% time API introduced in ERTS 7.0 and implement a fallback
+%% solution using the old primitives to be used on old ERTS
+%% versions. This way your code can automatically take advantage
+%% of the improvements in the API when available. This is an
+%% example of how to implement such an API, but it can be used
+%% as is if you want to. Just add (a preferrably renamed version of)
+%% this module to your project, and call the API via this module
+%% instead of calling the BIFs directly.
+%%
+
+-module(time_compat).
+
+%% We don't want warnings about the use of erlang:now/0 in
+%% this module.
+-compile(nowarn_deprecated_function).
+%%
+%% We don't use
+%%   -compile({nowarn_deprecated_function, [{erlang, now, 0}]}).
+%% since this will produce warnings when compiled on systems
+%% where it has not yet been deprecated.
+%%
+
+-export([monotonic_time/0,
+	 monotonic_time/1,
+	 erlang_system_time/0,
+	 erlang_system_time/1,
+	 os_system_time/0,
+	 os_system_time/1,
+	 time_offset/0,
+	 time_offset/1,
+	 convert_time_unit/3,
+	 timestamp/0,
+	 unique_integer/0,
+	 unique_integer/1,
+	 monitor/2,
+	 system_info/1,
+	 system_flag/2]).
+
+monotonic_time() ->
+    try
+	erlang:monotonic_time()
+    catch
+	error:undef ->
+	    %% Use Erlang system time as monotonic time
+	    erlang_system_time_fallback()
+    end.
+
+monotonic_time(Unit) ->
+    try
+	erlang:monotonic_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    %% Use Erlang system time as monotonic time
+	    STime = erlang_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+erlang_system_time() ->
+    try
+	erlang:system_time()
+    catch
+	error:undef ->
+	    erlang_system_time_fallback()
+    end.
+
+erlang_system_time(Unit) ->
+    try
+	erlang:system_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    STime = erlang_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+os_system_time() ->
+    try
+	os:system_time()
+    catch
+	error:undef ->
+	    os_system_time_fallback()
+    end.
+
+os_system_time(Unit) ->
+    try
+	os:system_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    STime = os_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+time_offset() ->
+    try
+	erlang:time_offset()
+    catch
+	error:undef ->
+	    %% Erlang system time and Erlang monotonic
+	    %% time are always aligned
+	    0
+    end.
+
+time_offset(Unit) ->
+    try
+	erlang:time_offset(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    try
+		_ = integer_time_unit(Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end,
+	    %% Erlang system time and Erlang monotonic
+	    %% time are always aligned
+	    0
+    end.
+
+convert_time_unit(Time, FromUnit, ToUnit) ->
+    try
+	erlang:convert_time_unit(Time, FromUnit, ToUnit)
+    catch
+	error:undef ->
+	    try
+		convert_time_unit_fallback(Time, FromUnit, ToUnit)
+	    catch
+		_:_ ->
+		    erlang:error(badarg, [Time, FromUnit, ToUnit])
+	    end;
+	error:Error ->
+	    erlang:error(Error, [Time, FromUnit, ToUnit])
+    end.
+
+timestamp() ->
+    try
+	erlang:timestamp()
+    catch
+	error:undef ->
+	    erlang:now()
+    end.
+
+unique_integer() ->
+    try
+	erlang:unique_integer()
+    catch
+	error:undef ->
+	    {MS, S, US} = erlang:now(),
+	    (MS*1000000+S)*1000000+US
+    end.
+
+unique_integer(Modifiers) ->
+    try
+	erlang:unique_integer(Modifiers)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Modifiers]);
+	error:undef ->
+	    case is_valid_modifier_list(Modifiers) of
+		true ->
+		    %% now() converted to an integer
+		    %% fullfill the requirements of
+		    %% all modifiers: unique, positive,
+		    %% and monotonic...
+		    {MS, S, US} = erlang:now(),
+		    (MS*1000000+S)*1000000+US;
+		false ->
+		    erlang:error(badarg, [Modifiers])
+	    end
+    end.
+
+monitor(Type, Item) ->
+    try
+	erlang:monitor(Type, Item)
+    catch
+	error:Error ->
+	    case {Error, Type, Item} of
+		{badarg, time_offset, clock_service} ->
+		    %% Time offset is final and will never change.
+		    %% Return a dummy reference, there will never
+		    %% be any need for 'CHANGE' messages...
+		    make_ref();
+		_ ->
+		    erlang:error(Error, [Type, Item])
+	    end
+    end.
+
+system_info(Item) ->
+    try
+	erlang:system_info(Item)
+    catch
+	error:badarg ->
+	    case Item of
+		time_correction ->
+		    case erlang:system_info(tolerant_timeofday) of
+			enabled -> true;
+			disabled -> false
+		    end;
+		time_warp_mode ->
+		    no_time_warp;
+		time_offset ->
+		    final;
+		NotSupArg when NotSupArg == os_monotonic_time_source;
+			       NotSupArg == os_system_time_source;
+			       NotSupArg == start_time;
+			       NotSupArg == end_time ->
+		    %% Cannot emulate this...
+		    erlang:error(notsup, [NotSupArg]);
+		_ ->
+		    erlang:error(badarg, [Item])
+	    end;
+	error:Error ->
+	    erlang:error(Error, [Item])
+    end.
+
+system_flag(Flag, Value) ->
+    try
+	erlang:system_flag(Flag, Value)
+    catch
+	error:Error ->
+	    case {Error, Flag, Value} of
+		{badarg, time_offset, finalize} ->
+		    %% Time offset is final
+		    final;
+		_ ->
+		    erlang:error(Error, [Flag, Value])
+	    end
+    end.
+
+%%
+%% Internal functions
+%%
+
+integer_time_unit(native) -> 1000*1000;
+integer_time_unit(nano_seconds) -> 1000*1000*1000;
+integer_time_unit(micro_seconds) -> 1000*1000;
+integer_time_unit(milli_seconds) -> 1000;
+integer_time_unit(seconds) -> 1;
+integer_time_unit(I) when is_integer(I), I > 0 -> I;
+integer_time_unit(BadRes) -> erlang:error(bad_time_unit, [BadRes]).
+
+erlang_system_time_fallback() ->
+    {MS, S, US} = erlang:now(),
+    (MS*1000000+S)*1000000+US.
+
+os_system_time_fallback() ->
+    {MS, S, US} = os:timestamp(),
+    (MS*1000000+S)*1000000+US.
+
+convert_time_unit_fallback(Time, FromUnit, ToUnit) ->
+    FU = integer_time_unit(FromUnit),
+    TU = integer_time_unit(ToUnit),
+    case Time < 0 of
+	true -> TU*Time - (FU - 1);
+	false -> TU*Time
+    end div FU.
+
+is_valid_modifier_list([positive|Ms]) ->
+    is_valid_modifier_list(Ms);
+is_valid_modifier_list([monotonic|Ms]) ->
+    is_valid_modifier_list(Ms);
+is_valid_modifier_list([]) ->
+    true;
+is_valid_modifier_list(_) ->
+    false.